We built a replacement server (x86_64) for an older server (x86).
Now we want to move a RAID-5 array intact from the older machine
over to the new machine. We know the UUID of the array and of all
the PV and VG on the array. So what commands should we perform
after plugging in all the array drives to the new server to bring
up the array and lvm on the new machine?

"vgscan" and "vgchange -a VGNAME" I believe.

Sorry, doing three things at once: vgchange -a y VGNAME

Make sure your VG name doesn't conflict with any already in the
machine.

Will vgchange activate the raid array?

Is it an md (software) RAID or a hardware RAID device?

If the former, then I'm not sure. I'll have to defer to someone with
more md experience.
If the latter, then it depends of if you have the correct drivers and
hardware detection.

The new server just has a couple raid-1 arrays on it right now. But
we need the raid-5 to be activated because there is a volgroup that
uses the raid-5 device as it's PV.